Lysine is an amino acid (building block of protein). People use it to make medicine. Lysine is used for preventing and treating cold sores (caused by the virus called herpes simplex labialis). It is taken by mouth or applied directly to the skin for this use.
Lysine (symbol Lys or K) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −COO− form under biological conditions), and a side chain lysyl ((CH2)4NH2), classifying it as a basic, charged (at physiological pH), aliphatic amino acid.
The human body cannot synthesize lysine, so it is essential in humans and must be obtained from the diet.
Lysine plays several roles in humans, most importantly proteinogenesis, but also in the crosslinking of collagen polypeptides, uptake of essential mineral nutrients, and in the production of carnitine, which is key in fatty acid metabolism.
Due to its importance in several biological processes, a lack of lysine can lead to several disease states including defective connective tissues, impaired fatty acid metabolism, anaemia, and systemic protein-energy deficiency. In contrast, an overabundance of lysine, caused by ineffective catabolism, can cause severe neurological issues.
Lysine can also contribute to protein stability as its ε-amino group often participates in hydrogen bonding, salt bridges and covalent interactions to form a Schiff base.
Lysine has also been implicated to play a key role in other biological processes including; structural proteins of connective tissues, calcium homeostasis, and fatty acid metabolism.
Because herpes simplex virus (HSV) proteins are richer in arginine and poorer in lysine than the cells they infect, lysine supplements have been tried as a treatment.
Lysine has also been shown to play a role in anaemia, as stated above, as lysine is suspected to have an effect on the uptake of iron and, subsequently, the concentration of ferritin in blood plasma.
Lysine production for animal feed is a major global industry, reaching in 2009 almost 700,000 tonnes for a market value of over €1.22 billion. Lysine is an important additive to animal feed because it is a limiting amino acid when optimizing the growth of certain animals such as pigs and chickens for the production of meat. Lysine supplementation allows for the use of lower-cost plant protein (maize, for instance, rather than soy) while maintaining high growth rates, and limiting the pollution from nitrogen excretion.